A need presently exists for a system for freezing boneless chicken products (e.g., marinaded or nonmarinaded chicken breast fillets) and other boneless food products whereby the resulting frozen products have highly uniform thickness profiles. A need particularly exists for such a freezing system wherein: (a) moisture and marinade losses are minimized; (b) when thawed, the products do not substantially spring back to their original thickness profile; (c) the natural shapes of the products, as viewed from the top and bottom thereof, are substantially maintained; (d) the surfaces of the frozen products are substantially free from marks, cracks, and other surface imperfections; (e) product breakage is minimized; and (f) freezing time is reduced.
The achievement of a highly uniform frozen product thickness profile is desirable for numerous reasons. For example, the achievement of a consistent, uniform, product thickness would provide a substantial health safety benefit by allowing more standardized product cooking procedures to be used. Additionally, the provision of a uniform frozen product thickness would improve the packaging characteristics of the frozen product and would improve product plate or bun coverage.
One system used heretofore for freezing boneless chicken fillets consists of a marination tub, a roller-type press, and a mechanical freezer. In this system, 40.degree. to 45.degree. F. marinaded product from the marination tub is conveyed through the roller-type press before being frozen in the mechanical freezer. The roller-type press is intended to operate as a means for imparting a uniform thickness profile to the product. Unfortunately, however, the compressed shape imparted by the roller-type press is only partially retained during the freezing process. Additionally, the amount of time required for mechanically freezing the product is undesirably high (i.e., typically about 40 minutes for marinaded chicken breast fillets). Also, due to marinade seepage and moisture loss, approximately 7 weight percent of the product is typically lost during the pressing and freezing operations. Further, due primarily to the number of product transfer points involved in this system and to the characteristics of the wire mesh conveyor systems typically used in mechanical freezers, the frozen product obtained from this prior art system is characterized by an undesirable degree of breakage and surface imperfections (e.g., cracks and freezer belt impressions).
Another system used heretofore for freezing boneless chicken breast fillets consists of a marination tub, a nitrogen bath, a roller-type press, and a mechanical freezer. This system is identical to the system just described except that, prior to being conveyed through the roller-type press, the food product is dipped in liquid nitrogen. Using this system, approximately 25% of the overall product Btu removal occurs in the nitrogen bath. Consequently, product residence time in the mechanical freezer is desirably reduced to about 30 to 35 minutes. Unfortunately, however, the use of a nitrogen bath provides only a slight improvement in product thickness profile retention. Further, the use of a nitrogen bath only slightly reduces yield losses, product breakage, and surface imperfections.